Device and method for detecting the phase of a signal

ABSTRACT

This invention relates to a device and method for estimating a phase reference or a phase shift of a S 1  with respect to another reference signal S 0 .

TECHNICAL FIELD AND BACKGROUND ART

This invention relates to a method and a device for extracting the phaseof a signal, possibly comprising noise, or a phase reference of amodulated signal, possibly comprising noise.

It is used particularly in applications in the domain of RFID (RadioFrequency IDentification) systems. An RFID system is usually formed froma first device containing stored data, usually called label, capable oftransmitting these data in the form of radio waves at a frequency withina range usually between a few kHz and a few MHz. A second read device isthen provided for acquisition of said stored data. To achieve thisacquisition, the second device is capable of emitting a signal S formedfrom a carrier. In response to this signal S, the first device thenemits another signal S′ containing said data. This other signal S′ isusually formed by a sub-carrier with a frequency proportional to thefrequency of said carrier, according to a predetermined protocol. Theother signal S′ may be modulated, for example using a phase modulation.

The read device should preferably be capable of detecting a phasereference of this other signal S′, so that the read device candemodulate the other signal S′. To achieve this, a number of cycles maybe specifically inserted at the beginning of the other signal S′ so thatthe read device will have the time to detect this phase reference. Oneknown method called the “correlation method” is currently used to dothis detection type. This method consists of multiplying one or severalcycles of said other signal S′, for which the phase reference issearched by one or several cycles of a reference signal S₀ with afrequency identical to the frequency of said sub-carrier.

The analogue or digital results obtained from these multiplications areintegrated over one or several periods. These operations are repeatedregularly in time and are a maximum at the instant at which the othersignal S′ and the reference signal S₀ are in phase. The moment at whichthis maximum occurs corresponds to an instant used as the phasereference for the other signal S′.

This method has the disadvantage that it lacks precision, particularlywhen the other signal S′ comprises noise. It also requires the use of alarge number of resources in the read device.

SUMMARY OF THE INVENTION

This invention proposes a method for estimating or measuring the phaseshift of a signal S₁, with a period approximately equal to a period Tswith respect to a reference signal S₀ with period Ts, comprising stepsconsisting of receiving the signal S₁ and starting a capture processincluding steps consisting of:

-   -   a) at instants regularly distributed within a first time        interval equal to the period Ts, carry out a sequence of n        detections of the state of the signal S₁, where n is an integer        greater than 1, and for each of these detections increasing a        given count variable in a sequence of n count variables, or        leaving it unchanged depending on the said state    -   b) reiterate step a) over one or several other time intervals,        each equal to the said first time interval,    -   c) stop the capture process at an end of capture instant        t_(end),    -   d) compare the corresponding values of count variables for        adjacent count means, in pairs in the said sequence of count        variables,    -   e) identify the two adjacent count variables x_(j) and x_(j+1)        with the greatest difference, among the differences between two        adjacent variables, where j is an integer.

The phase shift between the reference signal S₀ and the signal S₁ may beestimated after step e) by a phase shift value between (j/n)*2π and((j+1)/n)*2π, for example (j/n)*2π.

The processed signal S₁ may be a digital signal, digitized on one orseveral bits. This signal may also be a digital signal, obtained bydigitization of an analogue signal or by processing of an analoguesignal.

The signal S₁ may possibly be an analogue signal. In this case, aprocessing step of the signal S₁, for example using one or severalcomparators or using an analogue/digital converter, may be providedbefore starting the capture process.

In step a), the increase in a count variable may correspond to anincrement of said count variable by a fixed increment value, or by anincrement value that can vary as a function of said detected state.

For example, in the case in which the signal S₁ is digitized on severalbits and uses a signed logic, it would be possible that the incrementvalue is signed and that the sign of the increment value varies as afunction of the state of the detected signal S₁. It would also bepossible for the said increment value to vary as a function of the stateof the detected signal S₁ and the average value or the average state ofthe signal S₁ at the detection instant.

The increase of a count variable may also correspond to an operationother than an increment on this count variable. For example, it mayconsist of a multiplication of this variable by a value that depends onthe state of the detected signal S₁.

The capture process according to the invention may be reiterated for aninteger number of periods with duration Ts. According to one variant,the capture process done in step b) and in step c) may be reiterateduntil one of the said count variables reaches a value Xthreshold_1. Thisthreshold value Xthreshold_1 may be predetermined and fixed, oraccording to one variant it may be initialized to be equal to apredetermined value and then vary during the capture process, forexample as a function of the signal-to-noise ratio relative to thesignal S₁ and/or the information throughput relative to the signal S₁.

According to a second variant, the capture process may be reiterateduntil the difference in the count variable at the output from the twoadjacent count means reaches a threshold Xthreshold_2.

This threshold Xthreshold_2 may be predetermined and fixed, or accordingto one variant it may be initialized to be equal to a predeterminedvalue and then vary during said capture process, for example as afunction of the signal-to-noise ratio relative to signal S₁, or theinformation throughput carried by signal S₁.

The invention also relates to a method of reading a transponder or alabel comprising:

-   -   emission of a signal with a predetermined frequency, by a read        device,    -   reception of another signal S₁ emitted by the transponder or the        label, by the read device,    -   implementation of one of the previously described processes.

The signal S₀ may be generated by the read device, starting from saidsignal with a predetermined frequency, for example by frequency divisionof said signal, with a predetermined frequency or using a localoscillator integrated into the read device.

The invention also relates to a device for estimating the phase shift ofa signal S₁ with a period approximately equal to Ts with respect to areference signal S₀ with period Ts, comprising:

-   -   n count means, each of the count means when activated being        capable of detecting an instantaneous state of signal S₁ and        increasing a count variable with which it is associated among n        count variables, or leaving it unchanged, as a function of said        detected instantaneous state,    -   control means capable of periodically and successively        activating said n count means in a predetermined order, within a        time interval with a duration equal to the period Ts of the        signal S₀ and at regularly distributed instants in said time        interval,    -   comparator means capable of comparing the values of count        variables in each adjacent count means, among the n count        variables of the n count means, in pairs, and when the        comparison is made, the said comparator means determine the        greatest difference.

The phase shift estimating device according to the invention may alsocomprise:

-   -   means for estimating the phase shift between S₀ and S₁ as a        function of said greatest determined difference.

According to one particular embodiment of the device, when activated,each of the count means may be capable of detecting an instantaneousstate of the signal S₁ and incrementing a count variable with which itis associated among the n count variables, or leaving it unchanged, as afunction of said instantaneous detected state.

The device may also include means for determining the average value orthe average state M of the signal S₁. Each of the count means can thenbe designed so that when it is activated, it detects an instantaneousstate of the signal S₁ and increments a count variable with which it isassociated among N count variables, or leaves it unchanged, as afunction of said instantaneous detected state and said average value Mof the signal S₁.

Means for generating the signal S₀ with period T_(S) may also beintegrated into the device according to the invention. These means mayinclude an oscillator such as a clock and/or frequency division means.

BRIEF DESCRIPTION OF THE FIGURES

This invention will be better understood after reading the descriptionof example embodiments given purely for information and in no waylimitative, with reference to the appended figures, wherein:

FIG. 1 illustrates an example device implemented according to theinvention,

FIG. 2 illustrates a time diagram for operation of a device usedaccording to the invention,

FIG. 3 illustrates a variant of the device used according to theinvention.

Identical, similar or equivalent parts of the different figures aremarked with the same numeric references so as to facilitate comparisonbetween one figure and the next.

The different parts shown in the figures are not necessarily shown atthe same scale, to make the figures more easily understandable.

DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS

An example embodiment implemented according to the invention will now bedescribed with reference to FIG. 1. In particular, this device enablesdetermination in time of a phase reference instant, or it detects thephase of a signal S₁ with respect to a reference signal S₀ with periodTs, or it detects the phase shift of S₁ with respect to S₀.

The signal S₁ may for example be a digital signal, possibly comprisingnoise, with a period identical or similar to the period Ts of thereference signal S₀.

The signal S₁ may also for example be a digital signal with twomodulated states, for example phase modulated from a carrier with aperiod equal to the period Ts of the reference signal S₀.

The device implemented according to the invention comprises firstlycontrol means 110 receiving the input reference signal S₀, andperiodically and successively activating n different count means 100 ₀,. . . , 100 _(n−1) within a time interval with a duration equal to theperiod Ts of the signal S₀ and at regularly distributed instants withinthe said time interval.

According to one particular embodiment, means denoted 115, for examplein the form of a clock such as a piezoelectric based clock, may beintegrated into the said device to generate and send the referencesignal S₀ with period Ts, particularly at the input to control means110.

After the signal S₁ has been received at the input to said device andstarting from the moment at which this device begins to carry out aphase shift measurement process of the signal S₁, a given count means100 _(i) among the n count means 100 ₀, . . . 100 _(n−1) may beactivated, for example by control means 110 at instantst _(i) =t ₀ +i*(Ts/n)+k*Ts  (1).

In the expression reference (1), ‘t₀’ is a moment or instant at which aprocess for detection of the phase of signal S₁ begins. ‘i’ correspondsto the rank of the given count means 100 _(i), which is the i(th) countmeans making a detection in a time interval equal to Ts, after a firstcount means 100 ₀ has first made a detection within said time interval.‘n’ is the total number of count means 100 ₀, . . . , 100 _(n−1), and‘k’ is an integer corresponding to the total number of detections madeby the given count means 100 _(i).

The number n of count means may vary for example as a function of therequired detection precision. According to one particular embodiment,the number n of count means may be equal to a power of 2.

Each of the different count means 100 ₀, . . . , 100 _(n−1) isassociated with a count variable that it can modify and for which itproduces the output value. The different count means 100 ₀, . . . , 100_(n−1) produce the count variables x₀, . . . , x_(n−1) respectively atthe output. The operating means of each of them are identical.

When a given count means 100 i (iε[0;n−1]) is activated by the controlmeans 110 at a given time t_(i)(iε[0;n−1]), this given count means 100_(i) detects the state or the value of the signal S₁. The given countmeans 100 _(i) is then capable of modifying or not modifying a givencount variable x_(i) (iε[0;n−1]) with which it is associated and forwhich it produces the output value, depending on the detected state ofthe signal S₁.

The modification of the given count variable x_(i), if any, consists ofincreasing the count variable by incrementing it, for example by anincrement value Q₁.

Since the signal S₁ is a two-state signal, according to a first variantit would be possible, for example, for a given count means 100 _(i) toincrement the given count variable x_(i) with which it is associated, bythe increment value Q₁ when it detects a “high” state or a logical levelof the signal S₁ equal to ‘1’. According to this first variant, thegiven count means 100 _(i) leaves the given count variable x_(i) withwhich it is associated unchanged when it detects a “low” state or alogical level of the signal S₁ equal to ‘0’.

According to a second variant, it would be possible for example for thegiven count means 100 _(i) to increment the given count variable x_(i)with which it is associated, by the increment value Q₁, when it detectsa “low” state or a logical level of the signal S₁ equal to ‘0’.According to this second variant, the given count means 100 _(i) leavesthe given count variable x_(i) with which it is associated unchangedwhen it detects a “high” state or a logical level of the signal S₁ equalto ‘1’.

Since this signal S₁ is a two-state signal, the count means 100 ₀, . . ., 100 _(n−1), may be made for example from counters formed in a givenarrangement of logical gates.

Comparator means denoted 130 that can be connected to all the outputsfrom the different count means 100 ₀, . . . , 100 _(n−1) are used tocompare the value of each count variable with the value of each“adjacent” or “neighbor” count variable.

A given count means 100 _(i) will be called “neighbor” or “adjacent” toanother count means 100 _(j) when the said given count means is thecount means that has made a detection just before or just after theother said count means 100 _(j) among all of the count means 100 ₀, . .. , 100 _(n−1).

We will now present an example phase detection method according to theinvention performed by a device of the type mentioned above, but in thiscase provided with n=8 count means 100 ₀, . . . , 100 ₇, explicitly withreference to FIG. 2.

The objective is to detect the phase of the signal S₁ (step curvedenoted C₁) using the reference signal S₀ (not shown but for which theperiod is equal to Ts).

Operation of the different count means 100 ₀, . . . , 100 ₇ during timeis shown in FIG. 2, by time diagrams denoted Cpt₀, Cpt₁, Cpt₂, Cpt₃,Cpt₄, Cpt₅, Cpt₆, Cpt₇, respectively.

At a given start time denoted to after the signal S₁ has been receivedat the input to said device implemented according to the invention, aprocess to capture the phase shift of S₁ with respect to S₀ begins.

Then, starting from this start moment or instant to, within a first timeinterval ΔT₁ preferably equal to the period Ts of the reference signalS₀, the said control means 110 successively activate each of thedifferent count means 100 ₀, . . . , 100 ₇ from the first count means100 ₀ to the eighth count means 100 ₇ once only, at moments or instantsdenoted to, t₁, t₂, t₃, t₄, t₅, t₆, t₇, uniformly distributed during thesaid first time interval ΔT₁.

The count means 100 ₀, . . . , 100 ₇ each perform a single detection ofthe signal S₁ and modify or do not modify the values of theircorresponding count variables, once only, within the said first timeinterval ΔT₁.

The count means 100 ₀, . . . , 100 ₇, are thus used to save successiveimages of the state of the signal S₁. Some of the count means 100 ₀, . .. , 100 ₇ will have detected a given state of the signal S₁ during thefirst time interval ΔT₁. Other count means 100 ₀, . . . , 100 ₇ willhave detected another state of the signal S₁.

For example, at an instant or moment denoted t₃ (reference 200 on timediagram Cpt₃) within the time interval ΔT₁, the count means 100 ₃corresponding to the time diagram Cpt₃ has detected a <<low >> state ofthe signal S₁, the value of the count variable x₃ with which it isassociated then remains unchanged and equal to the value 0. At anotherinstant or moment denoted t₄ (reference 210 on time diagram Cpt₄) withinthe time interval ΔT₁, the count means 100 ₄ associated with the timediagram Cpt₄ has detected a <<high >> state of the signal S₁, the valueof the count variable x₄ with which it is associated is then incrementedand set equal to the value 1.

Since the first time interval ΔT₁, is equal to the period Ts of thesignal S₀, the phase reference or the phase origin of the signal S₁ isbetween two instants or moments t_(j) and t_(j+1) (where jε[0;6]) atwhich the signal S₁ is detected by two adjacent count means 100 j and100 j+1 respectively. At the end of the time interval ΔT₁, the said twoadjacent count means 100 j and 100 _(j+1) will have corresponding countvariables x_(j) and x_(j+1) with different values, one of the said twoadjacent count means having detected a certain logical state of thesignal for example a <<low >> state, and the other having detectedanother logical state of the signal, for example a <<high >> state.

Since the signal S₁ may comprise noise or a may be a modulated signalpossibly comprising noise, once the first time interval ΔT₁ has elapsed,the operation described above is preferably reiterated.

Then, in a second time interval ΔT₂ equal to Ts, the control means 110once again activate the different count means 100 ₀, . . . , 100 ₇, fromthe first count means 100 ₀ to the 8th count means 100 ₇, at uniformlydistributed instants in this second time interval ΔT₂ and in the sameorder as before.

In this second time interval ΔT₂, the detection instants or moments ofthe said two adjacent count means 100 _(j) and 100 _(j+1) occur at timest_(j)+Ts and t_(j+1)+Ts respectively, and then once again enclose thephase reference of the signal S₁ in time.

For example, at an instant denoted t₃+Ts (reference 220 on time diagramCpt₃), the count means 1003 corresponding to time diagram Cpt₃ hasdetected a <<low >> state of the signal S₁ within the time interval ΔT₂,the value of the count variable X₃ with which it is associated remainsunchanged and is equal to the value 0. The count means 100 ₄corresponding to time diagram Cpt₄ has detected a <<high >> state of thesignal S1 at another instant denoted t₄+Ts (reference 230 on timediagram Cpt₄) within the time interval ΔT₂, the value of the countvariable x₄ with which it is associated is then incremented and setequal to the value 2.

The operation carried out during the first time interval ΔT₁ and thenduring the second time interval ΔT₂ can thus be reiterated identicallyover several time intervals equal to the period Ts until the time tendthat will be called the end of capture time, at which the control means110 described above stop activating the count means 100 ₀, . . . , 100₇, and at which these count means stop modifying their correspondingcount variables. The total detection duration ΔT of the detectionprocess may for example be such that:

-   -   ΔT=m*Ts (where ‘m’ is an integer number, preferably more than        1).

Several variant embodiments may be provided to start the end of captureprocess described above.

According to a first variant, it will be possible that the captureprocess could for example be completed after a fixed predeterminedduration after the start instant to or a time that might vary, forexample as a function of several factors such as the informationthroughput carried by the signal S₁, the signal to noise ratio forsignal S₁.

According to a second variant illustrated on FIG. 3, specific meansdenoted 135 could be provided to trigger the end of capture process.

These means 135, for example formed by an arrangement of logical gates,can for example be used to compare the corresponding value of each ofthe count variables at the output from the different count means 100 ₀,. . . , 100 ₇, with a threshold Xthreshold_1. When a given countvariable x_(i) at the output from a given count means 100 _(i) reachesthe value of the threshold Xthreshold_1, the end of capture detectionmeans 130 emit an end of capture signal S_(end) at the output, forexample to control means 110 so that they stop activating the countmeans 100 ₀, . . . , 100 ₇, and possibly to comparator means 120 at theend of a complete cycle.

The threshold Xthreshold_1 may be a predetermined fixed value. Thethreshold Xthreshold_1 may also be a variable initialized to apredetermined value that is modified during the count process as afunction of one or several factors, for example such as the informationthroughput carried by the signal S₁, the signal to noise ratio relatedto signal S₁. The throughput is defined as the number of bits per second(bits that modulate the phase, in other words that carry theinformation).

When the end of capture instant t_(end) has occurred, the control means110 stop activating the count means 100 ₀, . . . , 100 ₇. Comparatormeans 130 like those described above are then used to compare the outputvalue of each count variable 100 ₀, . . . , 100 ₇ with the output valueof each “adjacent” or “neighbor” count variable and to identify the pairof adjacent count means with the greatest difference in count variables.

Instants or moments t_(j)+k₁*Ts and t_(j+1)+k₁*Ts (where j and k₁ areinteger numbers) at which each of the count means in said pair of countmeans have made their detections, enclose, in time, the phase referencemoment or instant. According to the previously described referenceexpression (1), the instants t_(j)+k₁*Ts and t_(j+1)+k₁*Ts coincide withinstants t₀+j*(Ts/n)+k*Ts and t₀+(j+1)*(Ts/n)+k*Ts respectively.

The phase shift between the signal S₀ and the signal S₁ can then beestimated to be equal to a value between (j*2π)/n and ((j+1)*2π)/n), forexample (j*2π)/n.

FIG. 2 shows an example count means 1003, the operation of which isillustrated by time diagram Cpt3 and the count means 1004, the operationof which is illustrated by time diagram Cpt₄. The count means 1003 andthe count means 1004 make their detections at instants t₃+k₁*Ts andt₄+k₁*Ts respectively, enclosing the phase reference time.

According to a third variant, the capture process described above may becompleted when the difference in the count variable at the output fromtwo adjacent count means, among all count means 100 ₀, . . . , 100 ₇,reaches a certain predetermined threshold Xthreshold_2.

In this third variant, the end of capture may be triggered for exampleby comparator means 130, or by other means provided for this purpose.The threshold Xthreshold_2 may be a fixed predetermined value. Thethreshold Xthreshold_2 may also be associated with a variableinitialized to a predetermined value and which is modified during thecount process for example as a function of one or several factors suchas the information throughput carried by the signal S₁, the signal tonoise ratio related to signal S₁.

The invention is not limited to detection of the phase of a digitalsignal and it can be applied to an analogue signal. Means, for examplein the form of a comparator or an analogue/digital converter, may thenbe included in the device used according to the invention so that saidanalogue signal can be modified or so that processing can be done on asignal with two or more states as described above.

The invention can also be applied to phase detection of a signalcomprising more than two logical states. It may be used to detect thephase of a signal S₁ digitized on several bits.

The detection principle may then be similar to that described above.

When a given count means 100 _(i) (iε[0;n−1]) is activated by controlmeans 110 at a given instant or moment t_(i), this given count means 100_(i) detects a state or a logical value of the signal S₁. The said givencount means 100 _(i) is then capable of modifying or not modifying agiven count variable x_(i) with which it is associated and for which itproduces the output value, depending on the detected state of the signalS₁.

If the given count variable x_(i) is modified, it consists ofincrementing this count variable by an increment value Q₂ that can varyas a function of the state of the detected signal S₂. The state of thesignal S₂ means the state of each of the bits forming the signal S₂.

This variant may be achieved for example using a device comprising anumber of inputs equal to the number of bits in the signal S₁. Each ofthe count means can then detect the state of each bit making up thesignal S₁.

For example, it would be possible for the count means to operateaccording to a signed logic:

For example, consider the case in which the signal S₂ is a signaldigitized on 3 bits denoted a₂a₁a₀ where a₂ is a high order bit. Itwould be possible according to a first variant that a given count means100 _(i) then increments the given count variable x_(i) with which it isassociated, by a value equal to −(a₁*2¹+a₀*2⁰), when it detects a stateor a logical level of the signal S₂ equal to ‘0a₁a₀’ and a value equalto +(a₁*2¹+a₀*2⁰) when it detects a state or logical level of the signalS₂ equal to ‘1a₁a₀’. The sign of the increment value Q₂ may thus dependon the state of the signal S₁.

In the examples described above, the count means of the device accordingto the invention are used such that every time that a given count meansdetects a signal, said count means increments a count variable withwhich it is associated by an increment value that may be fixed orvariable depending on the state of said signal, or leaves it unchanged.

This invention is not limited to these operating examples. The countmeans may be designed to perform more complex operations than a simpleincrement or summation during each detection. This means that thedifference between the different count variables can be amplified morequickly, and the duration of the detection process can be reduced.

More generally, the count means in the device according to the inventionmay for example be designed such that every time that a given countmeans detects a signal, it increases a count variable with which it isassociated or it leaves it unchanged. The increase may for example bemade by multiplying the variable by a number proportional to or equal tothe value of the state of the said signal during the detection, or byanother mathematical function that possibly depends on the state of thesignal at the instant or moment of the detection.

One particular application of the invention is in the domain of RFID(Radio Frequency IDentification) systems. A phase detection device usedaccording to the invention may for example be integrated into an RFIDread device for acquisition of data within another device, for examplein the form of a label or transponder, by exchange of radiofrequencysignals.

An RFID read device used according to the invention can then acquiredata in a label or a transponder, using the following procedure:

The read device according to the invention is capable of emitting asignal S, starting from a carrier with a given frequency.

In response to this carrier, the transponder or the label emits anotherphase modulated signal S₁. This other signal S₁ is usually formedaccording to predetermined protocol, from a sub-carrier with a frequencythat is sub-multiple of the frequency of the said carrier emitted by theread device.

The other signal S₁ may possibly comprise noise (phase skip, parasitepulses).

The said read device according to the invention is then capable ofcreating a signal S₀ with period Ts equal to the period of saidsub-carrier from which the signal S₁ emitted by the label of thetransponder is formed, so that the read device can read variations ofthe other signal S₁ emitted by the label or the transponder. Forexample, the signal S₀ may be formed from one or several piezoelectricbased clock as was mentioned above or by frequency division of thecarrier, using frequency division means. Thus, the frequency of thesub-carrier starting from which the other signal S₁ is formed, is knownto the read device. The phase origin or the phase reference of the othersignal S₁ remains to be determined, so that the other signal can bedemodulated.

In order to determine this phase origin, an estimate of the phase shiftbetween the reference signal S₀ and the signal S₁ can then be made usinga process like that described above. This phase shift estimate can thenbe used to generate a signal S′₀ with a period equal to the period Ts ofthe sub-carrier and synchronized with S₁ so as to determine the phasemodulations of S₁ that carries the information.

This process could begin as soon as the read device receives the signalS₁.

1. Method for estimating the phase shift of a signal S₁ with a periodapproximately equal to period Ts with respect to a reference signal S₀with period Ts, comprising steps consisting of receiving the signal S₁and starting a capture process including steps consisting of: a) atinstants regularly distributed within a first time interval equal to theperiod Ts, carry out a sequence of n detections of the state of thesignal S₁, where n is an integer greater than 1, and for each of thesedetections, increasing a given count variable in a sequence of n countvariables x₀, . . . , x_(n−1), or leaving it unchanged depending on saidstate, b) reiterate step a) over one or several other time intervals,each equal to said first time interval, c) stop the capture process atan end of capture instant t_(end), d) compare the corresponding valuesof count variables for adjacent count means, in pairs in the saidsequence of count variables x₀, . . . x_(n−1), e) identify the twoadjacent count variables x_(j) and x_(j+1) with the greatest difference,among the differences between two adjacent variables, where j is aninteger, f) calculate the phase shift between S₀ and S₁.
 2. Methodaccording to claim 1, the action to increment said count variable instep a) corresponding to an increment in said count variable by a fixedincrement value, or by an increment value that can vary as a function ofsaid detected state.
 3. Method according to claim 1, step a) beingreiterated for an integer number of periods with duration Ts.
 4. Methodaccording claim 1, the capture process being reiterated until one of thecount variables reaches a value Xthreshold_1, Xthreshold_1 beingpredetermined or/and may vary during said capture process.
 5. Methodaccording to claim 1 the capture process being reiterated until thedifference in the count variable at the output from two adjacent countmeans reaches a threshold Xthreshold_2, Xthreshold_2 being predeterminedor/and may vary during the said capture process.
 6. Method according toclaim 1, the signal S₁ being a digital signal.
 7. Method according toclaim 1, the digital signal being obtained by digitizing an analoguesignal.
 8. Method according to claim 1, the signal S₁ being an analoguesignal.
 9. Method according to claim 1, the signal S₁ being a signaldigitized on several bits.
 10. Method according to claim 1, the countmeans incrementing the count variable by an increment value Q₂ that canvary as a function of the state of the detected digitized signal. 11.Method according to claim 1, the phase shift being estimated by a valuechosen within an interval between (j/n)*2π and ((j+1)/n)*2π.
 12. Methodaccording to claim 1, a signal S₀ with period Ts being generated by theread device.
 13. Method for estimating the phase shift of a signal S₁with a period approximately equal to period Ts with respect to areference signal S₀ with period Ts, comprising steps consisting ofreceiving the signal S₁ and starting a capture process including stepsconsisting of: a) at instants regularly distributed within a first timeinterval equal to the period Ts, carry out a sequence of n detections ofthe state of the signal S₁, where n is an integer greater than 1, andfor each of these detections, increasing a given count variable in asequence of n count variables by a fixed increment value, or by anincrement value that can vary as a function of said detected state, orleaving this count value unchanged depending on said state, b) reiteratestep a) over one or several other time intervals, each equal to saidfirst time interval, until one of the count variables reaches a valueXthreshold_1 that can be predetermined or/and can vary during saidcapture process, or/and until the difference in the count variable atthe output from two adjacent count means reaches a thresholdXthreshold_2, that can be predetermined or/and can vary during the saidcapture process, c) stop the capture process at an end of capture timet_(end), d) compare the corresponding values of count variables foradjacent count means, in pairs in said sequence of count variables x₀, .. . , x_(n−1), e) identify the two adjacent count variables x_(j) andx_(j+1) with the greatest difference, among the differences between twoadjacent variables, where j is an integer, f) calculate the phase shiftbetween S₀ and S₁.
 14. Method of reading a transponder or a labelcomprising: emission of a signal with a predetermined frequency, by aread device, reception of another signal S₁ emitted by the transponderor the label, by the read device, implementation of a method accordingto one of claim 1 or
 13. 15. Device for estimating the phase shift of asignal S₁ with a period approximately equal to Ts with respect to areference signal S₀ with period Ts, comprising: n count means, each ofthe count means when activated being capable of detecting aninstantaneous state of signal S₁ and increasing a count variable withwhich it is associated among n count variables, or leaving it unchanged,as a function of said detected instantaneous state, control meanscapable of periodically and successively activating the said n countmeans in a predetermined order, within a time interval with a durationequal to the period Ts of the signal S₀ and at regularly distributedtimes in said time interval, comparator means capable of comparing thevalues of count variables in each adjacent count means, among the ncount variables of the n count means, in pairs, and when the comparisonis made, said comparator means determine the greatest difference, meanscapable of estimating the phase shift between S₀ and S₁ as a function ofthe said greatest determined difference.
 16. Device according to claim15, each of the count means, when activated, being capable of detectingan instantaneous state of the signal S₁ and incrementing a countvariable with which it is associated among the n count variables, orleaving it unchanged, as a function of said instantaneous detectedstate.
 17. Device according to claim 15, also including: means fordetermining the average value of the signal S₁, each of the count means,when activated, being capable of detecting an instantaneous state of thesignal S₁ and incrementing a count variable with which it is associatedamong the n count variables, or leaving it unchanged, as a function ofsaid instantaneous detected state and said average value of the signalS₁.
 18. Device according to claim 15, also including means capable ofgenerating a signal S₀ with period T_(s).
 19. Device according to claim15, including means capable of generating a signal S₀ with period T_(s),comprising a clock or/and frequency division means.
 20. Device forestimating the phase shift of a signal S₁ with a period approximatelyequal to Ts with respect to a reference signal S₀ with period Ts,comprising: means capable of generating a signal S₀ with period Ts, ncount means, each of the count means, when activated, being capable ofdetecting an instantaneous state of the signal S₁ and incrementing acount variable with which it is associated among the n count variables,or leaving this count variable unchanged, as a function of saidinstantaneous detected state, control means capable of periodically andsuccessively activating the said n count means in a predetermined order,within a time interval with a duration equal to the period Ts of thesignal S₀ and at regularly distributed instants in said time interval,comparator means capable of comparing the values of count variables ineach adjacent count means, among the n count variables of the n countmeans, in pairs, and when the comparison is made, said comparator meansdetermine the greatest difference, means capable of estimating the phaseshift between S₀ and S₁ as a function of the said greatest determineddifference.
 21. RFID (Radio Frequency IDentification) read device for atransponder or a label comprising: means capable of emitting signals tobe sent to a label or a transponder, means capable of receiving signalsS₁ originating from a label or a transponder a device according to oneof claims 15 or 20.